Fiscal Year 2017 has seen significant progress toward accomplishing all of the Specific Aims; some of this progress is detailed here. For Aim 1, the first project focuses on the early development of MS lesions. Previously, we studied two critical aspects of lesion development: the small veins around which white matter lesions form, and the spatiotemporal dynamics of vascular permeability as manifested in gadolinium-enhanced MRI. To understand whether the presence of a central vein may help distinguish MS lesions from their mimickers an idea that remains controversial and to which we only partially subscribe we previously developed a rapid imaging approach for clinical 3T MRI called FLAIR*. One study to assess the utility of FLAIR* for diagnosis and characterization of MS lesions have been published in the last year (3); we found that the FLAIR* technique is able to significantly improve diagnostic confidence in a variety of settings. The technique is now in use at several centers around the world, and with the North American Imaging in MS cooperative, we have published a set of guidelines for central vein detection (15) and are planning a multi-center clinical trial to assess whether FLAIR* allows earlier and more confident diagnosis of the disease. With respect to vascular permeability, we previously established that there are two spatiotemporal patterns in MS lesions: a centrifugal pattern, in which serum contents leak from the center of the lesion and then proceed outward, over the course of minutes to hours, to fill the entire lesion; and a centripetal pattern, in which serum contents first appear on the periphery of the lesion and then proceed inward. These findings have important implications for understanding lesion development and its association with blood-brain-barrier permeability. In further work, we described how these permeability patterns help to determine the fashion in which acute MS lesions evolve into their chronic counterparts. Specifically, we found that very early events, perhaps occurring within the first month after lesion formation, appear to determine the efficacy of tissue repair, possibly including remyelination. In the past year, we have published a paper describing the very-long-term (10-20-year) evolution of MS lesions, showing that most lesions shrink over time (17). This research is ongoing, and based on it we have started a clinical trial to test whether corticosteroids improve lesion repair, in collaboration with our colleagues in the NINDS Neuroimmunology Clinic. We are also planning additional clinical trials over the next several years. In the past year, we have increased our focus on the characterization of MS lesions affecting the cerebral cortex, which have proved difficult to detect by MRI (unlike their white matter counterparts). Our approach here has been to evaluate new MRI approaches with potentially higher sensitivity than previously described methods, taking advantage of the 7-tesla research system at NIH and of our collaborations with MRI pulse sequence developers at NIH, in the extramural community, and in industry. In the past year, we have published an initial study on cortical lesions in pediatric-onset MS (7), and we have contributed to the in-print debate about the importance of cortical lesions (14). We have also followed up our prior discovery of the imaging correlate of inflammation in the leptomeninges (the membranes that surround the brain) by reporting similar observations in other neuroinflammatory diseases (1). Additionally under Aim 1, we have completed and published work on the evolution of inflammatory demyelinating lesions in the brains of marmoset monkeys with experimental autoimmune encephalomyelitis (EAE). We previously demonstrated that the blood-brain barrier becomes locally permeable up to four weeks prior to the onset of demyelination, and we showed that this permeability is associated with a perivascular lymphocytic and mononuclear infiltrate with parenchymal activation of microglia and astrocytes. Ongoing experiments are designed to dissect the cellular and radiological correlates of neuroprotection and lesion repair in marmoset EAE in a fashion that will have direct implications for our human studies. Preliminary results indicate that the model recapitulates MS extremely well for this purpose. Finally, we completed recruitment of asymptomatic first-degree relatives of people with MS, as well as matched healthy volunteers, as part of the first stage of the nationwide Genes and Environment in Multiple Sclerosis (GEMS) study. This is a collaboration with colleagues at the Brigham & Womens Hospital of Harvard University and the University of Pittsburgh Medical Center (NCT01353547 and NCT01617395). At NIH, we characterized individuals possibly at relatively high and low risk for development of clinical MS, and in the past year we have published a paper describing our results (22). For Aim 2, work in the past year has continued to focus on development of methodology for radiological-pathological correlation studies, particularly in the marmoset EAE model. We implemented high-resolution imaging of formalin-fixed brains using a variety of MRI approaches and developed a system to use those images to guide the histopathological analysis. This is accomplished by generating 3D-printed brain-cutting boxes that allow precise sectioning of the brain, such that small lesions observed on MRI (either in vivo or postmortem) can be localized and studied. We have demonstrated the value of this system for analyzing areas of neocortical demyelination and leptomeningeal inflammation. We have further shown its ability to analyze tiny abnormal disease foci in the marmoset model (9), which we are in the process of characterizing relative to their cellular components and for the presence or absence of heavy metals. We continue to make improvements to the ways in which MS is imaged (4, 5, 6, 12, 21), focusing with our collaborators on harmonizing imaging across multiple centers (11, 18), and using our approaches to improve diagnostic accuracy (19) and uncover new findings in individual patients (8). We have recently reviewed our research in MS and other neuroinflammatory diseases (2, 10, 13, 16). Finally, we have weighed in on the ongoing controversy about gadolinium deposition in the brain (20) and have devoted some effort to studying this phenomenon in our own lab.